The present invention is directed to controls for air pulse type cleaners for bag type or cartridge type filter systems and, more particularly, to a trigger or indexing mechanism for such a system which is entirely mechanical.
Bag type air filter systems are used in dusty environments to remove particulates in industrial operations in which the dust can be an explosion or health hazard or damaging to equipment or manufactured products or simply environmentally undesirable. In a typical bag type filter system, sometimes referred to as a baghouse filter system, dust laden air is passed through a dusty air plenum having a plurality of filter bags supported by frames or cages. The filter bags are made of a fabric, paper, or the like and trap dust particles on their external surfaces, with the cleaned air exiting from the insides of the bags into a clean air plenum. To prevent clogging the filter bags from a layer of dust on the outer surfaces of the bags, pulses of air are periodically injected through the inner surfaces of the bags to dislodge some of the dust on the outer surfaces, which then settles to the floor of the dusty air plenum or a conveyor below the bags.
It will be appreciated that newer filter devices also are in use which can be substituted for filter bags or used in the alternative. This alternative filter medium is generally know as the filter cartridge. Such filter cartridges are comprised of a cloth or paper or synthetic filter medium which may or may not include a structural support such as a wire or plastic cage or frame or support. Throughout this specification it is to be understood that the use of the term “bag” or “bag type” or “filter bag” includes such filter cartridge units as an equivalent structure.
In a common type of bag filter arrangement, the bags are arranged in groups of a particular pattern in circumferentially spaced sectors of a cylindrical plenum. A radial distribution arm with nozzles arranged in a pattern to coincide with the positions of the bags in the sectors is rotated over the bags. A timing mechanism is synchronized in such a manner as to inject pulses of compressed air into the bags as the nozzle group passes over a group of bags. Since time is needed to refill an air tank with compressed air, the timing mechanism is arranged to skip a number of bag groups before the next group is cleaned. Thus, it takes several revolutions of the distribution arm to clean all the bags. Details of a typical arrangement of a bag filter system can be found in U.S. Pat. No. 4,655,799, which is incorporated herein by reference.
In U.S. Pat. No. 4,655,799, the air distribution arm extends radially from the air tank which is also rotated and into which compressed air is fed through a rotary union. A diaphragm type valve seats against an inner extension of the distribution arm and is operated by a secondary diaphragm valve in fluidic communication with a solenoid valve. The solenoid valve is controlled by a photoelectric cell through a counter which counts the passage of pegs on a peg wheel rotated synchronous with the rotating tank and arm and having a peg corresponding to each sector of bags. When the solenoid valve is opened, air in the secondary valve is released, thereby causing the main diaphragm valve to open temporarily against spring pressure and releasing air from the tank through the nozzles on the distribution arm. The counter controls the frequency of air pulses so that pulses are released for every third peg sensed. By this means, every third group of bags receives cleaning pulses, and if the number of sectors is not divisible by three, within three revolutions of the distribution arm, every sector group of bags will be cleaned.
The air tank is rotated in an arrangement such as the one shown in the U.S. Pat. No. 4,655,799, along with the secondary valve. For this reason, either a rotary air union is required between the secondary valve and the solenoid valve, or a rotary electrical connection is needed between the photoelectric cell and the rotated solenoid valve. Because of the complexity of such arrangements and/or the possibility of arcing at brushes of a rotary electrical connection, there is a need for a more simplified triggering mechanism for cleaning pulses for bag type filter systems.
FIG. 1 illustrates a prior art arrangement for triggering the release of cleaning pulses in a bag filter system which is entirely mechanical and which does not require rotary air or electrical connections. The trigger mechanism 200 includes a trigger frame 202 having a mounting clamp 204 slidably connected thereto. The clamp 204 is provided for securing the mechanism 200 to a shaft connected to a rotary compressed air tank so that the mechanism 200 is rotated therewith. The frame 202 has a trigger arm 206 pivotally connected at one end to the frame 202 and at the opposite end through a chain link 208 to a valve plunger 210. The valve plunger 210 is mounted for reciprocating movement and includes a valve head 212 which engages a valve seat formed within a bore 214 within the frame 202. The valve head 212 is urged toward the valve seat by a valve return spring 215 engaged between the valve head 212 and the frame 206. The bore 214 is threaded at one end to receive a fitting fluidically communicating with a pilot valve which operates a main diaphragm valve to release compressed air into a distribution arm. When the valve head 212 separates from the valve seat, pressurized air is released from the pilot valve which temporarily opens the main diaphragm valve. A pinion gear 216 is journaled on the frame 202 and has a coaxial rotary cam member 218 secured thereto and including a cam lobe 220. A cam follower roller 222 is rotatably mounted on the trigger arm 206 and is urged into engagement with the cam 218 by the valve return spring 215.
The pinion gear 216 engages a stationary spur gear mounted coaxial with the rotating air tank so that the pinion gear 216 rotates relative to the frame 216 as the tank is rotated. When the cam lobe 220 engages the follower 222, the trigger arm 206 is pivoted outward thereby drawing the valve head 212 out of seating engagement with the valve seat and releasing the pressure from the pilot valve. The gear ratio between the pinion gear 216 and the spur gear is selected to control the frequency of release of cleaning pulses. Similarly, the cam lobe 220 and frame 202 are positioned in such a manner as to synchronize opening of the valve 212 with the passage of nozzles of the distribution arm over a group of bags.
A problem with the trigger mechanism 200 is that the valve head 212 is maintained in a seated or sealed position entirely by the force of the valve return spring 215. Additionally, the relative sizing of the gears and the synchronization of the cam lobe are critical to assure that the air pulses are released at an optimum time with the nozzles centered over a group of bags or cartridges.